Advances in snowmobile technology have included electronic fuel injection, larger engines, and lighter weights. Some long-track snowmobiles develop more than 150 horsepower while weighing less than 500 pounds. Electronic fuel injection allows easy starts, consistent power, smooth idling regardless of elevation or temperature, and a light throttle pull. Improved engine performance and power-to-weight ratios have enabled snowmobiles with wide skis and long tracks to move through deep and steep snow.
However, certain snow conditions may hinder the exit of exhaust gases conventionally channeled out the bottom of the belly pan. The situation is compounded with larger engines; more air and fuel moves in and out of the engine. Thus, if the exhaust exit is blocked by snow, engine performance suffers. This phenomenon is known as “Capping off”.
Such blockages are more likely to occur in deep, non-compacted snow conditions into which today's lighter, more powerful snowmobiles may enter. The bottom of the belly pan may slide through non-compacted snow, or snow may restrict the exhaust exit port area under certain conditions of snow temperature, density, and moisture content. Either of these scenarios may restrict flow of exhaust gases, robbing the engine of power. The problem is amplified with a right-hand turn, as the under-belly outlet is typically under the right side of the snowmobile. The outlet is stuffed into the snow. This increases the back pressure of the exhaust system and causes the snowmobile engine to bog down and die out.
Attempts to maintain open flow have focused on deflecting the snow away from the outlet under the belly pan. However, the deflectors don't eliminate the “capping off” problem in deep snow, especially with a right-hand turn. Therefore, a need exists for an unrestricted exhaust exit port under all snow and riding conditions.